Products that allows users to transmit and receive data wirelessly at relatively high data rates are becoming common. One group of such products is known by the name WiMAX (Worldwide Interoperability for Microwave Access). Products that pass the conformity tests for WiMAX are capable of forming wireless connections between them to permit the carrying of internet packet data over relatively long distances.
IEEE802.16e is a standard under development that covers WiMAX broadband wireless access for fixed and mobile users. It is envisaged that a base station should be provided, having a fixed connection to a computer network such as the internet. System subscribers can then gain access to the computer network through the base station. Each base station must be able to provide service to multiple subscribers.
IEEE802.16e uses orthogonal frequency division multiplexing (OFDM) as the modulation technology. Symbols are created, each containing a number, N, of orthogonal carrier frequencies (referred to as subcarriers). Within a symbol, the different subcarriers carry nulls (to simplify filtering), pilot information (for channel estimation) or user data.
Orthogonal frequency division multiple access (OFDMA) is also used, allowing each symbol in the downlink (that is, the connection from the base station to user) to contain data for multiple users, i.e. the N subcarriers can be allocated to different users. To help achieve this, the subcarriers are grouped into subchannels, and one or more subchannels are allocated to each user.
However, the allocation of subcarriers to subchannels is not trivial. To help mitigate channel effects, the subcarriers allocated to a particular subchannel are spread throughout the symbol. To complicate things further, the allocation changes on alternate symbols as the subcarriers allocated to pilot information change. The IEEE802.16e specification details the permutation sequences, equations and look-up tables necessary to implement this mapping, but it provides no indication as to how to design the hardware implementation of such a system.
Therefore, broadband wireless base stations compliant with IEEE802.16e require a block to map data to be transmitted to different users into different subcarriers in the symbol to be transmitted. This block is referred to herein as a subchannelization module.